The present invention relates to a skin perfusion evaluation apparatus and method. More particularly, the present invention relates to an apparatus and method for rapidly assessing microvascular perfusion of the skin which is capable of providing an indication of vascular sufficiency in the tested area.
The apparatus of the present invention is particularly effective in early detection of pressure ulcers to permit treatment before such pressure ulcers (i.e. bed sores) develop. When a patient is bedridden, soft tissue is often compressed for a long period of time between a bone of the patient and a firm surface such as a mattress. This can cause a localized area of tissue necrosis also known as a pressure ulcer, decubitus ulcer, or bed sore.
It is known that temperature of the skin resulting from intrinsic or non-environmental factors is primarily produced by blood perfusion. The present invention provides a handheld mechanism for rapidly assessing perfusion of the skin. By determining the likelihood for development of pressure ulcers before the pressure ulcers actually occur, it is possible to take preventative steps to prevent pressure ulcers. For instance, the patient could be transferred to a different bed which reduces pressure on the body. The patient can be monitored more closely to make sure that pressure on a particularly vulnerable area is avoided. Therefore, by providing rapid assessment of microvascular perfusion in a particular area, the present invention can reduce the likelihood of development of pressure ulcers, thereby reducing pain and suffering to the patient and reducing costs associated with treating pressure ulcers after they develop.
The apparatus and method of the present invention is also useful for diabetics. The apparatus and method for evaluating skin perfusion can be used to monitor and detect vascular insufficiency in the legs before the insufficiencies lead to leg ulcers and other problems. The apparatus and method of the present invention is useful in any instance where determination of reduced blood flow in an area can result in earlier treatment (i.e. tissue flaps and grafts).
According to one aspect of the present invention, an apparatus is provided for evaluating perfusion adjacent a skin surface. The apparatus includes a thermoelectric device having a cold plate and a hot plate with a temperature differential therebetween. The thermoelectric device is mounted so that it can be positioned adjacent the region of the patient""s skin. The device includes a sensor for measuring the temperature differential between the cold plate and the hot plate and a controller coupled to the sensor in the thermoelectric device for maintaining the temperature differential substantially constant by providing electrical energy to the thermoelectric device. The electrical energy provided to the thermoelectric device when it is positioned adjacent the region of the patient""s skin is indicative of the perfusion capacity. Additionally, the cold plate may be positioned to lie between the patient""s skin and the hot plate when the thermoelectric device is positioned adjacent the region of the patient""s skin. A heat sink may be provided for maintaining the hot plate at the temperature substantially equal to the temperature of ambient air. The thermoelectric device may be a Peltier device. The device may include a DC power source electrically coupled to the thermoelectric device, and a gauge for measuring the electrical energy provided to the thermoelectric device.
According to another aspect of the present invention, a device for determining a perfusion capacity in a region of a patient""s skin and underlying tissue includes a plate mounted in a position permitting placement of the plate adjacent the region of the patient""s skin. A sensor is provided to determine the temperature of the plate and a controller is coupled to the sensor and to the plate to provide electrical energy to the plate to maintain the temperature of the plate substantially constant. The electrical energy provided to the plate when the plate is positioned adjacent the region of the patient""s skin is indicative of the perfusion capacity in the region of the patient""s skin and underlying tissue. The device may include a gauge coupled to the controller for measuring the energy required to maintain the temperature of the plate substantially constant. The device may also include a second plate spaced apart from and thermally coupled to the first plate by a boundary so that providing electrical energy to the first and second plates induces heat to cross the boundary between the first plate and the second plate. A heat sink may be provided for dissipating heat transferred from the first plate to the second plate so as to maintain the temperature of the second plate at the temperature of the ambient air.
According to yet another aspect of the present invention, a device for determining perfusion capacity at a region of the patient""s skin and underlying tissue includes a first plate mounted to be placed in a position adjacent the region of the patient""s skin and a second plate electrically coupled to the first plate by a junction containing material dissimilar to one of the first and second plates. A controller maintains a first plate at a first temperature and the second plate at a second temperature defining a temperature differential which is maintained substantially constant by the controller by adjusting electrical energy supplied to the first and second plates. The electrical energy supplied to the first and second plates when the first plate is positioned adjacent the region of the patient""s skin is indicative of the perfusion capacity of the region of the patient""s skin and underlying tissue. The device may include a heat exchanger which maintains the second plate at the temperature of ambient air. A fan can be provided to force ambient air across the heat exchanger. The device may include a power source providing direct current flowing between the first and second plates, which current may flow in the direction which induces the first plate to have a temperature lower than the temperature of the second plate.
According to another aspect of the present invention, a method is provided for evaluating microvascular perfusion adjacent a skin surface. The method includes a step of thermally coupling a plate to a region of the patient""s skin and providing energy to the plate to dissipate heat absorbed by the plate from the skin. The provided energy is measured and used to calculate the perfusion capacity. The method may include the step of establishing an initial temperature of the plate before thermally coupling the plate to the region of the patient""s skin. This initial temperature may be lower than the temperature of the ambient air adjacent the patient""s skin. The method may include providing electrical energy so as to substantially dissipate all of the heat absorbed by the first plate. This energy may be provided until the rate at which the energy is provided reaches a steady state value.
According to yet another aspect of the present invention, a method for using a first plate and a second plate and the differential temperature therebetween to determine the perfusion capacity of a region of a patient""s skin and underlying tissue utilizes plates that are juxtaposed and configured such that heat applied to the first plate relative to the second plate will provide an electrical measurement. The method includes placing the first plate adjacent to the region of the patient""s skin, providing an electrical measurement indicative of the energy affecting the differential temperature, and providing an indication of the perfusion capacity related to the energy affecting the differential temperature. The energy affecting the differential temperature may be an energy required to maintain the differential temperatures substantially constant. The method may also include the step of allowing the energy affecting the differential temperature to reach a steady state value after the first plate is placed adjacent to the region of the patient""s skin. The method may also include the step of maintaining the second plate at a substantially constant temperature.
According to still another aspect of the present invention, a method for using the Peltier Effect (xe2x80x9cPExe2x80x9d) to determine a perfusion capacity of a region of the patient""s skin and underlying tissue includes steps of providing a PE sensor having a first plate to be thermally coupled to the region of the patient""s skin and a second plate spaced apart from the first plate and a controller for applying a current across the plates. The first plate is thermally coupled to the patient""s skin and the current required to maintain the temperature of the first plate at a setpoint temperature is measured. The current measurement is used to provide an indication of the perfusion capacity. The method may include the step of cooling the first plate to the setpoint temperature which is lower than the expected temperature of the region of the patient""s skin by applying a current to the plates prior to thermally coupling the first plate to the region of the patient""s skin. The method may also include the step of measuring the current required to maintain the temperature of the first plate at the setpoint temperature to determine a baseline current value prior to thermally coupling the first plate to the region of the patient""s skin. The method may also include the step of permitting the measured current to reach a substantially steady state value after thermally coupling the first plate to the region of the patient""s skin and comparing the substantially steady state value of the measured current to the baseline current value to provide an indication of perfusion capacity. The thermal coupling of the first plate to the region of the patient""s skin may be maintained until the substantially steady state current value is compared to the baseline current value.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.